Bulk polymerization of conjugated dienes using a nickel-based catalyst system

ABSTRACT

A process for preparing a polydiene, the process comprising the steps of (i) providing conjugated diene monomer; (ii) charging a nickel-based catalyst system to the conjugated diene monomer; and (iii) charging a modulating Lewis base to the conjugated diene monomer, to thereby polymerize the conjugated diene monomer in the presence of the modulating Lewis base, where said step of charging a modulating Lewis base is separate from said step of charging a nickel-based catalyst, and where said steps of providing conjugated diene monomer, charging a nickel-based catalyst system and charging a Lewis base form a polymerization mixture that includes less than 20% by weight of organic solvent based on the total weight of the polymerization mixture.

This application claims the benefit of U.S. Provisional Application Ser.No. 61/428,924, filed Dec. 31, 2010, which is incorporated herein byreference.

FIELD OF THE INVENTION

One or more embodiments of the present invention relate to a method forthe bulk polymerization of conjugated dienes by employing a nickel-basedcatalyst system in the presence of a modulating Lewis base.

BACKGROUND OF THE INVENTION

Synthetically produced polymers such as polydienes are used in the artof manufacturing tires. Synthetic polymers that undergo strain-inducedcrystallization provide advantageous properties such as tensile strengthand abrasion resistance. Thus, cis-1,4-polydienes with highcis-1,4-linkage content, which exhibit the increased ability to undergostrain-induced crystallization, have been advantageously employed.

Polydienes may be produced by solution polymerization, whereinconjugated diene monomer is polymerized in an inert solvent or diluent.The solvent serves to solubilize the reactants and products, to act as acarrier for the reactants and product, to aid in the transfer of theheat of polymerization, and to help in moderating the polymerizationrate. The solvent also allows easier stirring and transferring of thepolymerization mixture (also called cement), since the viscosity of thecement is decreased by the presence of the solvent. Nevertheless, thepresence of solvent presents a number of difficulties. The solvent mustbe separated from the polymer and then recycled for reuse or otherwisedisposed of as waste. The cost of recovering and recycling the solventadds greatly to the cost of the polymer being produced, and there isalways the risk that the recycled solvent after purification may stillretain some impurities that will poison the polymerization catalyst. Inaddition, some solvents such as aromatic hydrocarbons can raiseenvironmental concerns. Further, the purity of the polymer product maybe affected if there are difficulties in removing the solvent.

Polydienes may also be produced by bulk polymerization (also called masspolymerization), wherein conjugated diene monomer is polymerized in theabsence or substantial absence of any solvent, and, in effect, themonomer itself acts as a diluent. Since bulk polymerization isessentially solventless, there is less contamination risk, and theproduct separation is simplified. Bulk polymerization offers a number ofeconomic advantages including lower capital cost for new plant capacity,lower energy cost to operate, and fewer people to operate. Thesolventless feature also provides environmental advantages, withemissions and waste water pollution being reduced.

Despite its many advantages, bulk polymerization requires very carefultemperature control, and there is also the need for strong and elaboratestirring equipment since the viscosity of the polymerization mixture canbecome very high. In the absence of added diluent, the high cementviscosity and exotherm effects can make temperature control verydifficult. Consequently, local hot spots may occur, resulting indegradation, gelation, and/or discoloration of the polymer product. Inthe extreme case, uncontrolled acceleration of the polymerization ratecan lead to disastrous “runaway” reactions. To facilitate thetemperature control during bulk polymerization, it is desirable that acatalyst gives a reaction rate that is sufficiently fast for economicalreasons but is slow enough to allow for the removal of the heat from thepolymerization exotherm in order to ensure the process safety.

Nickel-based catalyst systems including a nickel-containing compound, anorganoaluminum compound, and a fluorine-containing compound may beemployed for polymerizing conjugated dienes to form cis-1,4-polydienes.The fluorine-containing compounds may include boron trifluoride andcomplexes of boron trifluoride with monohydric alcohols, phenols, water,mineral acids, ketones, esters, ethers, and nitriles.

EP 0 236 257 teaches a method for the bulk polymerization of1,3-butadiene into cis-1,4-polybutadiene by using a nickel-basedcatalyst system. The method includes very rapid polymerization of1,3-butadiene to achieve a conversion of at least 60% in a short periodof time. The molecular weight of the resulting cis-1,4-polybutadiene isreduced by employing a molecular weight regulator such as 1-butene.Actual practice of the invention, as shown in the examples, shows thatthe polymerization takes place at a relatively high temperature (e.g.,50° C.) to give cis-1,4-polybutadiene having a relatively high Mooneyviscosity (ML₁₊₄@100° C.) (e.g., 82) and relatively high molecularweight distribution (e.g., greater than 2.9).

SUMMARY OF THE INVENTION

One or more embodiments of the present invention provide a process forpreparing a polydiene, the process comprising the steps of (i) providingconjugated diene monomer; (ii) charging a nickel-based catalyst systemto the conjugated diene monomer; and (iii) charging a modulating Lewisbase to the conjugated diene monomer, to thereby polymerize theconjugated diene monomer in the presence of the modulating Lewis base,where said step of charging a modulating Lewis base is separate fromsaid step of charging a nickel-based catalyst, and where said steps ofproviding conjugated diene monomer, charging a nickel-based catalystsystem and charging a Lewis base form a polymerization mixture thatincludes less than 20% by weight of organic solvent based on the totalweight of the polymerization mixture.

One or more embodiments of the present invention also provide a processfor preparing a polydiene, the process comprising the step of forming apolymerization mixture by introducing a nickel-based catalyst system anda modulating Lewis base to conjugated diene monomer, where thepolymerization mixture includes less than about 20% by weight of organicsolvent, and where the modulating Lewis base is introduced directly andindividually to the conjugated diene monomer.

One or more embodiments of the present invention also provide a processfor producing a polydiene, the process comprising the step ofpolymerizing conjugated diene monomer in the presence of a catalyticallyeffective amount of an active nickel-based catalyst and a modulatingLewis base, where the modulating Lewis base is introduced directly andindividually to the conjugated diene monomer, and where said step ofpolymerizing takes place within a polymerization mixture that includesless than 20% by weight of organic solvent based on the total weight ofthe polymerization mixture.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Embodiments of this invention are based, at least in part, on thediscovery of a process for producing high cis-1,4-polydienes by bulkpolymerization of conjugated dienes with a nickel-based catalyst systemin the presence of a modulating Lewis base. While the prior artcontemplates bulk polymerization of conjugated diene into highcis-1,4-polydienes using a nickel-based catalyst system, it has now beenobserved that by operating the bulk polymerization at high temperatures,reactor fouling is problematic and leads to broad molecular weightdistribution, high gel content, and/or undesirable Mooney viscosities.Practice of the present invention unexpectedly overcomes these problems.It is believed that the presence of the Lewis base modulates thepolymerization process, resulting in a process that has less reactorfouling, and produces polymers with narrow molecular weightdistribution, low gel content, and desirable Mooney viscosity even athigh polymerization temperatures. Advantageously, these benefits havebeen achieved in the absence of molecular weight regulators such as1-butene.

Examples of conjugated diene monomer include 1,3-butadiene, isoprene,1,3-pentadiene, 1,3-hexadiene, 2,3-dimethyl-1,3-butadiene,2-ethyl-1,3-butadiene, 2-methyl-1,3-pentadiene, 3-methyl-1,3-pentadiene,4-methyl-1,3-pentadiene, and 2,4-hexadiene. Mixtures of two or moreconjugated dienes may also be utilized in copolymerization.

In general, the nickel-based catalyst system employed in practicing thepresent invention may include the combination of or reaction product ofingredients including (a) a nickel-containing compound, (b) analkylating agent, and (c) a fluorine source. In certain embodiments,these catalyst compositions are devoid or substantially devoid of otherconstituents such as Lewis bases or Lewis acids.

As mentioned above, the catalyst system employed in the presentinvention include a nickel-containing compound. Variousnickel-containing compounds or mixtures thereof can be employed. In oneor more embodiments, these nickel-containing compounds may be soluble inhydrocarbon solvents such as aromatic hydrocarbons, aliphatichydrocarbons, or cycloaliphatic hydrocarbons. In other embodiments,hydrocarbon-insoluble nickel-containing compounds, which can besuspended in the polymerization medium to form catalytically activespecies, may also be useful.

The nickel atom in the nickel-containing compounds can be in variousoxidation states including but not limited to the 0, +2, +3, and +4oxidation states. Suitable nickel-containing compounds include, but arenot limited to, nickel carboxylates, nickel carboxylate borates, nickelorganophosphates, nickel organophosphonates, nickel organophosphinates,nickel carbamates, nickel dithiocarbamates, nickel xanthates, nickelβ-diketonates, nickel alkoxides or aryloxides, nickel halides, nickelpseudo-halides, nickel oxyhalides, and organonickel compounds.

Suitable nickel carboxylates include nickel formate, nickel acetate,nickel acrylate, nickel methacrylate, nickel valerate, nickel gluconate,nickel citrate, nickel fumarate, nickel lactate, nickel maleate, nickeloxalate, nickel 2-ethylhexanoate, nickel neodecanoate, nickelnaphthenate, nickel stearate, nickel oleate, nickel benzoate, and nickelpicolinate.

Suitable nickel carboxylate borates include compounds defined by theformulae (RCOONiO)₃B or (RCOONiO)₂B(OR), where each R, which may be thesame or different, is a hydrogen atom or a mono-valent organic group. Inone embodiment, each R may be a hydrocarbyl group such as, but notlimited to, alkyl, cycloalkyl, substituted cycloalkyl, alkenyl,cycloalkenyl, substituted cycloalkenyl, aryl, substituted aryl, aralkyl,alkaryl, allyl, and alkynyl groups, with each group preferablycontaining from 1 carbon atom, or the appropriate minimum number ofcarbon atoms to form the group, up to about 20 carbon atoms. Thesehydrocarbyl groups may contain heteroatoms such as, but not limited to,nitrogen, oxygen, silicon, sulfur, and phosphorus atoms. Nickelcarboxylate borate may include those disclosed in U.S. Pat. No.4,522,988, which is incorporated herein by reference. Specific examplesof nickel carboxylate borate include nickel(II) neodecanoate borate,nickel(II) hexanoate borate, nickel(II) naphthenate borate, nickel(II)stearate borate, nickel(II) octoate borate, nickel(II) 2-ethylhexanoateborate, and mixtures thereof.

Suitable nickel organophosphates include nickel dibutyl phosphate,nickel dipentyl phosphate, nickel dihexyl phosphate, nickel diheptylphosphate, nickel dioctyl phosphate, nickelbis(1-methylheptyl)phosphate, nickel bis(2-ethylhexyl) phosphate, nickeldidecyl phosphate, nickel didodecyl phosphate, nickel dioctadecylphosphate, nickel dioleyl phosphate, nickel diphenyl phosphate, nickelbis(p-nonylphenyl) phosphate, nickel butyl (2-ethylhexyl)phosphate,nickel (1-methylheptyl) (2-ethylhexyl)phosphate, and nickel(2-ethylhexyl) (p-nonylphenyl) phosphate.

Suitable nickel organophosphonates include nickel butyl phosphonate,nickel pentyl phosphonate, nickel hexyl phosphonate, nickel heptylphosphonate, nickel octyl phosphonate, nickel (1-methylheptyl)phosphonate, nickel (2-ethylhexyl) phosphonate, nickel decylphosphonate, nickel dodecyl phosphonate, nickel octadecyl phosphonate,nickel oleyl phosphonate, nickel phenyl phosphonate, nickel(p-nonylphenyl) phosphonate, nickel butyl butylphosphonate, nickelpentyl pentylphosphonate, nickel hexyl hexylphosphonate, nickel heptylheptylphosphonate, nickel octyl octylphosphonate, nickel(1-methylheptyl) (1-methylheptyl)phosphonate, nickel (2-ethylhexyl)(2-ethylhexyl)phosphonate, nickel decyl decylphosphonate, nickel dodecyldodecylphosphonate, nickel octadecyl octadecylphosphonate, nickel oleyloleylphosphonate, nickel phenyl phenylphosphonate, nickel(p-nonylphenyl) (p-nonylphenyl)phosphonate, nickel butyl(2-ethylhexyl)phosphonate, nickel (2-ethylhexyl) butylphosphonate,nickel (1-methylheptyl) (2-ethylhexyl)phosphonate, nickel (2-ethylhexyl)(1-methylheptyl)phosphonate, nickel (2-ethylhexyl)(p-nonylphenyl)phosphonate, and nickel (p-nonylphenyl)(2-ethylhexyl)phosphonate.

Suitable nickel organophosphinates include nickel butylphosphinate,nickel pentylphosphinate, nickel hexylphosphinate, nickelheptylphosphinate, nickel octylphosphinate, nickel (1-methylheptyl)phosphinate, nickel (2-ethylhexyl)phosphinate, nickel decylphosphinate,nickel dodecylphosphinate, nickel octadecylphosphinate, nickeloleylphosphinate, nickel phenylphosphinate, nickel(p-nonylphenyl)phosphinate, nickel dibutylphosphinate, nickeldipentylphosphinate, nickel dihexylphosphinate, nickeldiheptylphosphinate, nickel dioctylphosphinate, nickelbis(1-methylheptyl) phosphinate, nickel bis(2-ethylhexyl)phosphinate,nickel didecylphosphinate, nickel didodecylphosphinate, nickeldioctadecylphosphinate, nickel dioleylphosphinate, nickeldiphenylphosphinate, nickel bis(p-nonylphenyl)phosphinate, nickelbutyl(2-ethylhexyl)phosphinate, nickel(1-methylheptyl)(2-ethylhexyl)phosphinate, and nickel (2-ethylhexyl)(p-nonylphenyl) phosphinate.

Suitable nickel carbamates include nickel dimethylcarbamate, nickeldiethylcarbamate, nickel diisopropylcarbamate, nickel dibutylcarbamate,and nickel dibenzylcarbamate.

Suitable nickel dithiocarbamates include nickel dimethyldithiocarbamate,nickel diethyldithiocarbamate, nickel diisopropyldithiocarbamate, nickeldibutyldithiocarbamate, and nickel dibenzyldithiocarbamate.

Suitable nickel xanthates include nickel methylxanthate, nickelethylxanthate, nickel isopropylxanthate, nickel butylxanthate, andnickel benzylxanthate.

Suitable nickel β-diketonates include nickel acetylacetonate, nickeltrifluoroacetylacetonate, nickel hexafluoroacetylacetonate, nickelbenzoylacetonate, and nickel 2,2,6,6-tetramethyl-3,5-heptanedionate.

Suitable nickel alkoxides or aryloxides include nickel methoxide, nickelethoxide, nickel isopropoxide, nickel 2-ethylhexoxide, nickel phenoxide,nickel nonylphenoxide, and nickel naphthoxide.

Suitable nickel halides include nickel fluoride, nickel chloride, nickelbromide, and nickel iodide; suitable nickel pseudo-halides includenickel cyanide, nickel cyanate, nickel thiocyanate, nickel azide, andnickel ferrocyanide; and suitable nickel oxyhalides include nickeloxyfluoride, nickel oxychloride, and nickel oxybromide. In certainembodiments, a Lewis base such as tetrahydrofuran or an alcohol may beused as an aid for solubilizing these classes of nickel-containingcompounds in inert organic solvents. Where nickel fluoride, nickeloxyfluoride, or other nickel-containing compounds containing a fluorineatom are employed, the nickel-containing compounds may also serve aspart of the fluorine source in the above-mentioned catalyst system.

The term organonickel compound may refer to any nickel compoundcontaining at least one nickel-carbon bond. Suitable organonickelcompounds include bis(cyclopentadienyl)nickel (also called nickelocene),bis(pentamethylcyclopentadienyl)nickel (also calleddecamethylnickelocene), bis(tetramethylcyclopentadienyl)nickel,bis(ethylcyclopentadienyl)nickel, bis(isopropylcyclopentadienyl)nickel,bis(pentadienyl)nickel, bis(2,4-dimethylpentadienyl)nickel,(cyclopentadienyl) (pentadienyl)nickel, bis(1,5-cyclooctadiene)nickel,bis(allyl)nickel, bis(methallyl)nickel, and bis(crotyl)nickel.

As mentioned above, the nickel-based catalyst system employed in thepresent invention can include an alkylating agent. In one or moreembodiments, alkylating agents, which may also be referred to ashydrocarbylating agents, include organometallic compounds that cantransfer one or more hydrocarbyl groups to another metal. Typically,these agents include organometallic compounds of electropositive metalssuch as Groups 1, 2, and 3 metals (Groups IA, IIA, and IIIA metals).Alkylating agents useful in the present invention include, but are notlimited to, organoaluminum and organomagnesium compounds. As usedherein, the term organoaluminum compound refers to any aluminum compoundcontaining at least one aluminum-carbon bond. In one or moreembodiments, organoaluminum compounds that are soluble in a hydrocarbonsolvent can be employed. As used herein, the term organomagnesiumcompound refers to any magnesium compound that contains at least onemagnesium-carbon bond. In one or more embodiments, organomagnesiumcompounds that are soluble in a hydrocarbon can be employed. As will bedescribed in more detail below, several species of suitable alkylatingagents can be in the form of a fluoride compound. Where the alkylatingagent includes a fluorine atom, the alkylating agent may also serve asall or part of the fluorine source in the above-mentioned catalystsystem.

In one or more embodiments, organoaluminum compounds that can beutilized include those represented by the general formulaAlR_(n)X_(3−n), where each R independently can be a monovalent organicgroup that is attached to the aluminum atom via a carbon atom, whereeach X independently can be a hydrogen atom, a halogen atom (e.g., afluorine, chlorine, bromine, or iodine atom), a carboxylate group, analkoxide group, or an aryloxide group, and where n can be an integer inthe range of from 1 to 3. Where the organoaluminum compound includes afluorine atom, the organoaluminum compound can serve as both thealkylating agent and at least a portion of the fluorine source in thecatalyst system. In one or more embodiments, each R independently can bea hydrocarbyl group such as, for example, alkyl, cycloalkyl, substitutedcycloalkyl, alkenyl, cycloalkenyl, substituted cycloalkenyl, aryl,substituted aryl, aralkyl, alkaryl, allyl, and alkynyl groups, with eachgroup containing in the range of from 1 carbon atom, or the appropriateminimum number of carbon atoms to form the group, up to about 20 carbonatoms. These hydrocarbyl groups may contain heteroatoms including, butnot limited to, nitrogen, oxygen, boron, silicon, sulfur, and phosphorusatoms.

Types of the organoaluminum compounds that are represented by thegeneral formula AlR_(n)X_(3−n) include, but are not limited to,trihydrocarbylaluminum, dihydrocarbylaluminum hydride,hydrocarbylaluminum dihydride, dihydrocarbylaluminum carboxylate,hydrocarbylaluminum bis(carboxylate), dihydrocarbylaluminum alkoxide,hydrocarbylaluminum dialkoxide, dihydrocarbylaluminum halide,hydrocarbylaluminum dihalide, dihydrocarbylaluminum aryloxide, andhydrocarbylaluminum diaryloxide compounds. In one embodiment, thealkylating agent can comprise trihydrocarbylaluminum,dihydrocarbylaluminum hydride, and/or hydrocarbylaluminum dihydridecompounds.

Suitable trihydrocarbylaluminum compounds include, but are not limitedto, trimethylaluminum, triethylaluminum, triisobutylaluminum,tri-n-propylaluminum, triisopropylaluminum, tri-n-butylaluminum,tri-t-butylaluminum, tri-n-pentylaluminum, trineopentylaluminum,tri-n-hexylaluminum, tri-n-octylaluminum, tris (2-ethylhexyl)aluminum,tricyclohexylaluminum, tris (1-methylcyclopentyl)aluminum,triphenylaluminum, tri-p-tolylaluminum, tris(2,6-dimethylphenyl)aluminum, tribenzylaluminum, diethylphenylaluminum,diethyl-p-tolylaluminum, diethylbenzylaluminum, ethyldiphenylaluminum,ethyldi-p-tolylaluminum, and ethyldibenzylaluminum.

Suitable dihydrocarbylaluminum hydride compounds include, but are notlimited to, diethylaluminum hydride, di-n-propylaluminum hydride,diisopropylaluminum hydride, di-n-butylaluminum hydride,diisobutylaluminum hydride, di-n-octylaluminum hydride, diphenylaluminumhydride, di-p-tolylaluminum hydride, dibenzylaluminum hydride,phenylethylaluminum hydride, phenyl-n-propylaluminum hydride,phenylisopropylaluminum hydride, phenyl-n-butylaluminum hydride,phenylisobutylaluminum hydride, phenyl-n-octylaluminum hydride,p-tolylethylaluminum hydride, p-tolyl-n-propylaluminum hydride,p-tolylisopropylaluminum hydride, p-tolyl-n-butylaluminum hydride,p-tolylisobutylaluminum hydride, p-tolyl-n-octylaluminum hydride,benzylethylaluminum hydride, benzyl-n-propylaluminum hydride,benzylisopropylaluminum hydride, benzyl-n-butylaluminum hydride,benzylisobutylaluminum hydride, and benzyl-n-octylaluminum hydride.

Suitable hydrocarbylaluminum dihydrides include, but are not limited to,ethylaluminum dihydride, n-propylaluminum dihydride, isopropylaluminumdihydride, n-butylaluminum dihydride, isobutylaluminum dihydride, andn-octylaluminum dihydride.

Suitable dihydrocarbylaluminum halide compounds include, but are notlimited to, diethylaluminum chloride, di-n-propylaluminum chloride,diisopropylaluminum chloride, di-n-butylaluminum chloride,diisobutylaluminum chloride, di-n-octylaluminum chloride,diphenylaluminum chloride, di-p-tolylaluminum chloride, dibenzylaluminumchloride, phenylethylaluminum chloride, phenyl-n-propylaluminumchloride, phenylisopropylaluminum chloride, phenyl-n-butylaluminumchloride, phenylisobutylaluminum chloride, phenyl-n-octylaluminumchloride, p-tolylethylaluminum chloride, p-tolyl-n-propylaluminumchloride, p-tolylisopropylaluminum chloride, p-tolyl-n-butylaluminumchloride, p-tolylisobutylaluminum chloride, p-tolyl-n-octylaluminumchloride, benzylethylaluminum chloride, benzyl-n-propylaluminumchloride, benzylisopropylaluminum chloride, benzyl-n-butylaluminumchloride, benzylisobutylaluminum chloride, benzyl-n-octylaluminumchloride, diethylaluminum fluoride, di-n-propylaluminum fluoride,diisopropylaluminum fluoride, di-n-butylaluminum fluoride,diisobutylaluminum fluoride, di-n-octylaluminum fluoride,diphenylaluminum fluoride, di-p-tolylaluminum fluoride, dibenzylaluminumfluoride, phenylethylaluminum fluoride, phenyl-n-propylaluminumfluoride, phenylisopropylaluminum fluoride, phenyl-n-butylaluminumfluoride, phenylisobutylaluminum fluoride, phenyl-n-octylaluminumfluoride, p-tolylethylaluminum fluoride, p-tolyl-n-propylaluminumfluoride, p-tolylisopropylaluminum fluoride, p-tolyl-n-butylaluminumfluoride, p-tolylisobutylaluminum fluoride, p-tolyl-n-octylaluminumfluoride, benzylethylaluminum fluoride, benzyl-n-propylaluminumfluoride, benzylisopropylaluminum fluoride, benzyl-n-butylaluminumfluoride, benzylisobutylaluminum fluoride, and benzyl-n-octylaluminumfluoride.

Suitable hydrocarbylaluminum dihalide compounds include, but are notlimited to, ethylaluminum dichloride, n-propylaluminum dichloride,isopropylaluminum dichloride, n-butylaluminum dichloride,isobutylaluminum dichloride, n-octylaluminum dichloride, ethylaluminumdifluoride, n-propylaluminum difluoride, isopropylaluminum difluoride,n-butylaluminum difluoride, isobutylaluminum difluoride, andn-octylaluminum difluoride.

Other organoaluminum compounds useful as alkylating agents that may berepresented by the general formula AlR_(n)X_(3−n) include, but are notlimited to, dimethylaluminum hexanoate, diethylaluminum octoate,diisobutylaluminum 2-ethylhexanoate, dimethylaluminum neodecanoate,diethylaluminum stearate, diisobutylaluminum oleate, methylaluminumbis(hexanoate), ethylaluminum bis(octoate), isobutylaluminumbis(2-ethylhexanoate), methylaluminum bis(neodecanoate), ethylaluminumbis(stearate), isobutylaluminum bis(oleate), dimethylaluminum methoxide,diethylaluminum methoxide, diisobutylaluminum methoxide,dimethylaluminum ethoxide, diethylaluminum ethoxide, diisobutylaluminumethoxide, dimethylaluminum phenoxide, diethylaluminum phenoxide,diisobutylaluminum phenoxide, methylaluminum dimethoxide, ethylaluminumdimethoxide, isobutylaluminum dimethoxide, methylaluminum diethoxide,ethylaluminum diethoxide, isobutylaluminum diethoxide, methylaluminumdiphenoxide, ethylaluminum diphenoxide, and isobutylaluminumdiphenoxide.

Another class of organoaluminum compounds suitable for use as analkylating agent in the present invention is aluminoxanes. Aluminoxanescan comprise oligomeric linear aluminoxanes, which can be represented bythe general formula:

and oligomeric cyclic aluminoxanes, which can be represented by thegeneral formula:

where x can be an integer in the range of from 1 to about 100, or about10 to about 50; y can be an integer in the range of from 2 to about 100,or about 3 to about 20; and where each R independently can be amonovalent organic group that is attached to the aluminum atom via acarbon atom. In one embodiment, each R independently can be ahydrocarbyl group including, but not limited to, alkyl, cycloalkyl,substituted cycloalkyl, alkenyl, cycloalkenyl, substituted cycloalkenyl,aryl, substituted aryl, aralkyl, alkaryl, allyl, and alkynyl groups,with each group containing in the range of from 1 carbon atom, or theappropriate minimum number of carbon atoms to form the group, up toabout 20 carbon atoms. These hydrocarbyl groups may also containheteroatoms including, but not limited to, nitrogen, oxygen, boron,silicon, sulfur, and phosphorus atoms. It should be noted that thenumber of moles of the aluminoxane as used in this application refers tothe number of moles of the aluminum atoms rather than the number ofmoles of the oligomeric aluminoxane molecules. This convention iscommonly employed in the art of catalyst systems utilizing aluminoxanes.

Aluminoxanes can be prepared by reacting trihydrocarbylaluminumcompounds with water. This reaction can be preformed according to knownmethods, such as, for example, (1) a method in which thetrihydrocarbylaluminum compound is dissolved in an organic solvent andthen contacted with water, (2) a method in which thetrihydrocarbylaluminum compound is reacted with water of crystallizationcontained in, for example, metal salts, or water adsorbed in inorganicor organic compounds, or (3) a method in which thetrihydrocarbylaluminum compound is reacted with water in the presence ofthe monomer or monomer solution that is to be polymerized.

Suitable aluminoxane compounds include, but are not limited to,methylaluminoxane (“MAO”), modified methylaluminoxane (“MMAO”),ethylaluminoxane, n-propylaluminoxane, isopropylaluminoxane,butylaluminoxane, isobutylaluminoxane, n-pentylaluminoxane,neopentylaluminoxane, n-hexylaluminoxane, n-octylaluminoxane,2-ethylhexylaluminoxane, cyclohexylaluminoxane,1-methylcyclopentylaluminoxane, phenylaluminoxane, and2,6-dimethylphenylaluminoxane. Modified methylaluminoxane can be formedby substituting about 20 to 80 percent of the methyl groups ofmethylaluminoxane with C₂ to C₁₂ hydrocarbyl groups, preferably withisobutyl groups, by using techniques known to those skilled in the art.

Aluminoxanes can be used alone or in combination with otherorganoaluminum compounds. In one embodiment, methylaluminoxane and atleast one other organoaluminum compound (e.g., AlR_(n)X_(3−n)), such asdiisobutyl aluminum hydride, can be employed in combination. U.S.Publication No. 2008/0182954, which is incorporated herein by referencein its entirety, provides other examples where aluminoxanes andorganoaluminum compounds can be employed in combination.

As mentioned above, alkylating agents useful in the present inventioncan comprise organomagnesium compounds. In one or more embodiments,organomagnesium compounds that can be utilized include those representedby the general formula MgR₂, where each R independently can be amonovalent organic group that is attached to the magnesium atom via acarbon atom. In one or more embodiments, each R independently can be ahydrocarbyl group including, but not limited to, alkyl, cycloalkyl,substituted cycloalkyl, alkenyl, cycloalkenyl, substituted cycloalkenyl,aryl, allyl, substituted aryl, aralkyl, alkaryl, and alkynyl groups,with each group containing in the range of from 1 carbon atom, or theappropriate minimum number of carbon atoms to form the group, up toabout 20 carbon atoms. These hydrocarbyl groups may also containheteroatoms including, but not limited to, nitrogen, oxygen, silicon,sulfur, and phosphorus atoms.

Suitable organomagnesium compounds that may be represented by thegeneral formula MgR₂ include, but are not limited to, diethylmagnesium,di-n-propylmagnesium, diisopropylmagnesium, dibutylmagnesium,dihexylmagnesium, diphenylmagnesium, and dibenzylmagnesium.

Another class of organomagnesium compounds that can be utilized as analkylating agent may be represented by the general formula RMgX, where Rcan be a monovalent organic group that is attached to the magnesium atomvia a carbon atom, and X can be a hydrogen atom, a halogen atom (e.g., afluorine, chlorine, bromine, or iodine atom), a carboxylate group, analkoxide group, or an aryloxide group. Where the organomagnesiumcompound includes a fluorine atom, the organomagnesium compound canserve as both the alkylating agent and at least a portion of thefluorine source in the catalyst system. In one or more embodiments, Rcan be a hydrocarbyl group including, but not limited to, alkyl,cycloalkyl, substituted cycloalkyl, alkenyl, cycloalkenyl, substitutedcycloalkenyl, aryl, allyl, substituted aryl, aralkyl, alkaryl, andalkynyl groups, with each group containing in the range of from 1 carbonatom, or the appropriate minimum number of carbon atoms to form thegroup, up to about 20 carbon atoms. These hydrocarbyl groups may alsocontain heteroatoms including, but not limited to, nitrogen, oxygen,boron, silicon, sulfur, and phosphorus atoms. In one embodiment, X canbe a carboxylate group, an alkoxide group, or an aryloxide group, witheach group containing in the range of from 1 to about 20 carbon atoms.

Types of organomagnesium compounds that may be represented by thegeneral formula RMgX include, but are not limited to,hydrocarbylmagnesium hydride, hydrocarbylmagnesium halide,hydrocarbylmagnesium carboxylate, hydrocarbylmagnesium alkoxide, andhydrocarbylmagnesium aryloxide.

Suitable organomagnesium compounds that may be represented by thegeneral formula RMgX include, but are not limited to, methylmagnesiumhydride, ethylmagnesium hydride, butylmagnesium hydride, hexylmagnesiumhydride, phenylmagnesium hydride, benzylmagnesium hydride,methylmagnesium chloride, ethylmagnesium chloride, butylmagnesiumchloride, hexylmagnesium chloride, phenylmagnesium chloride,benzylmagnesium chloride, methylmagnesium bromide, ethylmagnesiumbromide, butylmagnesium bromide, hexylmagnesium bromide, phenylmagnesiumbromide, benzylmagnesium bromide, methylmagnesium fluoride,ethylmagnesium fluoride, butylmagnesium fluoride, hexylmagnesiumfluoride, phenylmagnesium fluoride, benzylmagnesium fluoride,methylmagnesium hexanoate, ethylmagnesium hexanoate, butylmagnesiumhexanoate, hexylmagnesium hexanoate, phenylmagnesium hexanoate,benzylmagnesium hexanoate, methylmagnesium ethoxide, ethylmagnesiumethoxide, butylmagnesium ethoxide, hexylmagnesium ethoxide,phenylmagnesium ethoxide, benzylmagnesium ethoxide, methylmagnesiumphenoxide, ethylmagnesium phenoxide, butylmagnesium phenoxide,hexylmagnesium phenoxide, phenylmagnesium phenoxide, and benzylmagnesiumphenoxide.

As mentioned above, the nickel-based catalyst system employed in thepresent invention can include a fluorine source. As used herein, theterm fluorine source refers to any substance including at least onefluorine atom. In one or more embodiments, at least a portion of thefluorine source can be provided by either of the above-describednickel-containing compound and/or the above-described alkylating agent,when those compounds contain at least one fluorine atom. In other words,the nickel-containing compound can serve as both the nickel-containingcompound and at least a portion of the fluorine source. Similarly, thealkylating agent can serve as both the alkylating agent and at least aportion of the fluorine source.

In one or more embodiments, at least a portion of the fluorine sourcecan be present in the catalyst system in the form of a separate anddistinct fluorine-containing compound. Fluorine-containing compounds mayinclude various compounds, or mixtures thereof, that contain one or morelabile fluorine atoms. In one or more embodiments, thefluorine-containing compound may be soluble in a hydrocarbon solvent. Inother embodiments, hydrocarbon-insoluble fluorine-containing compoundmay be useful.

Types of fluorine-containing compounds include, but are not limited to,elemental fluorine, halogen fluorides, hydrogen fluoride, organicfluorides, inorganic fluorides, metallic fluorides, organometallicfluorides, and mixtures thereof. In one or more embodiments, complexesof the fluorine-containing compounds with a Lewis base such as ethers,alcohols, water, aldehydes, ketones, esters, nitriles, or mixturesthereof may be employed. Specific examples of these complexes includethe complexes of boron trifluoride or hydrogen fluoride with a Lewisbase such as hexanol.

Halogen fluorides may include iodine monofluoride, iodine trifluoride,and iodine pentafluoride.

Organic fluorides may include t-butyl fluoride, allyl fluoride, benzylfluoride, fluoro-di-phenylmethane, triphenylmethyl fluoride, benzylidenefluoride, methyltrifluorosilane, phenyltrifluorosilane,dimethyldifluorosilane, diphenyldifluorosilane, trimethylfluorosilane,benzoyl fluoride, propionyl fluoride, and methyl fluoroformate.

Inorganic fluorides may include phosphorus trifluoride, phosphoruspentafluoride, phosphorus oxyfluoride, boron trifluoride, silicontetrafluoride, arsenic trifluoride, selenium tetrafluoride, andtellurium tetrafluoride.

Metallic fluorides may include tin tetrafluoride, aluminum trifluoride,antimony trifluoride, antimony pentafluoride, gallium trifluoride,indium trifluoride, titanium tetrafluoride, and zinc difluoride.

Organometallic fluorides may include dimethylaluminum fluoride,diethylaluminum fluoride, methylaluminum difluoride, ethylaluminumdifluoride, methylaluminum sesquifluoride, ethylaluminum sesquifluoride,isobutylaluminum sesquifluoride, methylmagnesium fluoride,ethylmagnesium fluoride, butylmagnesium fluoride, phenylmagnesiumfluoride, benzylmagnesium fluoride, trimethyltin fluoride, triethyltinfluoride, di-t-butyltin difluoride, dibutyltin difluoride, andtributyltin fluoride.

An active catalyst is formed when the nickel-containing compound, thealkylating agent, and the fluorine source are introduced or broughttogether. The resulting active catalyst is capable of polymerizingconjugated diene monomer to form a high cis-1,4-polydiene under bulkpolymerization conditions.

Although one or more active catalyst species are believed to result fromthe combination of the catalyst ingredients, the degree of interactionor reaction between the various catalyst ingredients or components isnot known with any great degree of certainty. Therefore, the term activecatalyst or catalyst composition has been employed to encompass a simplemixture of the ingredients, a complex of the various ingredients that iscaused by physical or chemical forces of attraction, a chemical reactionproduct of the ingredients, or a combination of the foregoingingredients, so long as this mixture, complex, reaction product, orcombination is capable of polymerizing monomer as discussed above.

The foregoing nickel-based catalyst composition may have high catalyticactivity for polymerizing conjugated dienes into cis-1,4-polydienes overa wide range of catalyst concentrations and catalyst ingredient ratios.Several factors may impact the optimum concentration of any one of thecatalyst ingredients. For example, because the catalyst ingredients mayinteract to form an active species, the optimum concentration for anyone catalyst ingredient may be dependent upon the concentrations of theother catalyst ingredients.

In one or more embodiments, the molar ratio of the alkylating agent tothe nickel-containing compound (alkylating agent/Ni) can be varied fromabout 10:1 to about 50:1, in other embodiments from about 20:1 to about40:1, and in other embodiments from about 25:1 to about 35:1. In one ormore embodiments, the molar ratio of the alkylating agent to thenickel-containing compound (alkylating agent/Ni) is less than 35:1, inother embodiments less than 30:1, in other embodiments less than 27:1,and in other embodiments less than 25:1.

In one or more embodiments, the molar ratio of the fluorine source tothe nickel-containing compound is best described in terms of the ratioof the mole of fluorine atoms in the fluorine source to the mole ofnickel atoms in the nickel-containing compound (fluorine/Ni). In one ormore embodiments, the fluorine/Ni molar ratio can be varied from about70:1 to about 130:1, in other embodiments from about 80:1 to about120:1, and in other embodiments from about 90:1 to about 108:1.

In one or more embodiments, the molar ratio of the alkylating agent tothe fluorine source, which may be described in terms of the ratio of themole of alkylating agent to the mole of fluorine atoms in the fluorinesource (alkylating/fluorine), can be varied from 0.05:1 to 1.5:1, inother embodiments from 0.1:1 to 0.9:1, and in other embodiments from0.2:1 to 0.5:1.

The active catalyst can be formed by various methods.

In one or more embodiments, the active catalyst may be preformed. Thatis, the catalyst ingredients are pre-mixed outside the polymerizationsystem either in the absence of any monomer or in the presence of asmall amount of at least one conjugated diene monomer at an appropriatetemperature, which may be from about −20° C. to about 80° C. Theresulting catalyst composition may be aged, if desired, prior to beingadded to the monomer that is to be polymerized. As used herein,reference to a small amount of monomer refers to a catalyst loading ofgreater than 2 mmol, in other embodiments greater than 3 mmol, and inother embodiments greater than 4 mmol of nickel-containing compound per100 g of monomer during the catalyst formation.

In other embodiments, the active catalyst may be formed in situ byadding the catalyst ingredients, in either a stepwise or simultaneousmanner, to the monomer to be polymerized. In one embodiment, thealkylating agent can be added first, followed by the nickel-containingcompound, and then followed by the fluorine source. In one or moreembodiments, two of the catalyst ingredients can be pre-combined priorto being added to the monomer. For example, the nickel-containingcompound and the alkylating agent can be pre-combined and added as asingle stream to the monomer. Alternatively, the fluorine source and thealkylating agent can be pre-combined and added as a single stream to themonomer. An in situ formation of the catalyst may be characterized by acatalyst loading of less than 2 mmol, in other embodiments less than 1mmol, in other embodiments less than 0.2 mmol, in other embodiments lessthan 0.1 mmol, in other embodiments less than 0.05 mmol, and in otherembodiments less than or equal to 0.006 mmol of nickel-containingcompound per 100 g of monomer during the catalyst formation.

In one or more embodiments, the polymerization of conjugated dienemonomer with the nickel-based catalyst system is conducted in thepresence of a modulating Lewis base. As used herein, the term modulatingLewis base refers to any Lewis base that, when present in thepolymerization mixture, can modulate the polymerization to allow it toproceed at a reduced polymerization rate. In one or more embodiments, amodulating Lewis base includes a Lewis base that does not include anacidic proton.

In one or more embodiments, the modulating Lewis base is introduceddirectly and individually to the monomer to be polymerized or thepolymerization mixture. In other words, prior to being introduced to thepolymerization system, the modulating Lewis base is not complexed withthe various catalyst ingredients employed. In these or otherembodiments, alkylation of the nickel-containing compound, which isbelieved to take place when the nickel-containing compound and thealkylating agent are brought into contact, takes place in thesubstantial absence of the modulating Lewis base. In particularembodiments, the formation of the active catalyst takes place in thesubstantial absence of the modulating Lewis base.

As used herein, reference to a substantial absence refers to that amountof the modulating Lewis base or less that will not deleteriously impactthe formation or performance of the catalyst. In one or moreembodiments, the active catalyst is formed in the presence of less than10 mole, in other embodiments in the presence of less than 2 mole, andin other embodiments in the presence of less than 1 mole of themodulating Lewis base per mole of nickel metal in the nickel-containingcompound. In other embodiments, the catalyst is formed in the essentialabsence of the modulating Lewis base, which refers to a de minimisamount or less of the modulating Lewis base. In particular embodiments,the active catalyst is formed in the complete absence of the modulatingLewis base.

In one or more embodiments, the modulating Lewis base may be present inthe monomer prior to the introduction of the active catalyst, whichwould include a preformed active catalyst. For example, the modulatingLewis base is introduced directly and individually to the monomer to bepolymerized, and then the preformed active catalyst is introduced to themixture of the monomer and modulating Lewis base. In these embodiments,the introduction of the modulating Lewis base to the monomer to bepolymerized forms a monomer/modulating Lewis base blend that is free ofactive catalyst prior to the introduction of the active catalyst.

In other embodiments, the preformed active catalyst and the modulatingLewis base may be added simultaneously, yet separately and individually,to the monomer to be polymerized.

In other embodiments, the modulating Lewis base is introduced to themonomer that contains the active catalyst. As described above, theactive catalyst may be formed by a preforming procedure or in situ. Asthose skilled in the art appreciate, where the active catalyst ispresent in the monomer prior to the introduction of the modulating Lewisbase, the active catalyst may be in the form of propagating oligomericspecies at the time the modulating Lewis base is introduced. In thisregard, those skilled in the art will appreciate that reference toactive catalyst may refer to low molecular weight living orpseudo-living oligomers.

In one or more embodiments, the modulating Lewis base is introduced tothe monomer after introduction of the catalyst ingredients for formingthe active catalyst or introduction of the preformed active catalystitself. In one or more embodiments, the modulating Lewis base is addedbefore 5%, in other embodiments before 3%, in other embodiments before1%, and in other embodiments before 0.5% of the monomer is polymerized.

Exemplary modulating Lewis bases include, but are not limited to,dihydrocarbyl ethers and amines.

In one or more embodiments, suitable dihydrocarbyl ethers include thosecompounds represented by the formula R—O—R, where each R isindependently a hydrocarbyl group or substituted hydrocarbyl group. Thehydrocarbyl group may contain heteroatoms such as, but not limited to,nitrogen, oxygen, silicon, tin, sulfur, boron, and phosphorous atoms.Suitable types of hydrocarbyl groups or substituted hydrocarbyl groupsinclude, but are not limited to, alkyl, cycloalkyl, substitutedcycloalkyl, alkenyl, cycloalkenyl, aryl, substituted aryl groups, andheterocyclic groups.

Exemplary alkyl groups include methyl, ethyl, n-propyl, isopropyl,n-butyl, isobutyl, t-butyl, n-pentyl, isopentyl, neopentyl, n-hexyl,n-heptyl, 2-ethylhexyl, n-octyl, n-nonyl, and n-decyl groups.

Exemplary cycloalkyl groups include cyclopropyl, cyclobutyl,cyclopentyl, cyclohexyl, 2-methylcyclohexyl, 2-t-butylcyclohexyl, and4-t-butylcyclohexyl groups.

Exemplary aryl groups include phenyl, substituted phenyl, biphenyl,substituted biphenyl, bicyclic aryl, substituted bicyclic aryl,polycyclic aryl, and substituted polycyclic aryl groups. Substitutedaryl groups include those where a hydrogen atom is replaced by amono-valent organic group such as a hydrocarbyl group.

Exemplary substituted phenyl groups include 2-methylphenyl,3-methylphenyl, 4-methylphenyl, 2,3-dimethylphenyl, 3,4-dimethylphenyl,2,5-dimethylphenyl, 2,6-dimethylphenyl, and 2,4,6-trimethylphenyl (alsocalled mesityl) groups.

Exemplary bicyclic or polycyclic aryl groups include 1-naphthyl,2-napthyl, 9-anthryl, 9-phenanthryl, 2-benzo[b]thienyl,3-benzo[b]thienyl, 2-naphtho[2,3-b]thienyl, 2-thianthrenyl,1-isobenzofuranyl, 2-xanthenyl, 2-phenoxathiinyl, 2-indolizinyl,N-methyl-2-indolyl, N-methyl-indazol-3-yl, N-methyl-8-purinyl,3-isoquinolyl, 2-quinolyl, 3-cinnolinyl, 2-pteridinyl,N-methyl-2-carbazolyl, N-methyl-β-carbolin-3-yl, 3-phenanthridinyl,2-acridinyl, 1-phthalazinyl, 1,8-naphthyridin-2-yl, 2-quinoxalinyl,2-quinazolinyl, 1,7-phenanthrolin-3-yl, 1-phenazinyl,N-methyl-2-phenothiazinyl, 2-phenarsazinyl, and N-methyl-2-phenoxazinylgroups.

Exemplary heterocyclic groups include 2-thienyl, 3-thienyl, 2-furyl,3-furyl, N-methyl-2-pyrrolyl, N-methyl-3-pyrrolyl,N-methyl-2-imidazolyl, 1-pyrazolyl, N-methyl-3-pyrazolyl,N-methyl-4-pyrazolyl, 2-pyridyl, 3-pyridyl, 4-pyridyl, pyrazinyl,2-pyrimidinyl, 3-pyridazinyl, 3-isothiazolyl, 3-isoxazolyl, 3-furazanyl,2-triazinyl, morpholinyl, thiomorpholinyl, piperidinyl, piperazinyl,pyrrolidinyl, pyrrolinyl, imidazolidinyl, and imidazolinyl groups.

Suitable types of dihydrocarbyl ethers include, but are not limited to,dialkyl ethers, dicycloalkyl ethers, diaryl ethers, and mixeddihydrocarbyl ethers.

Specific examples of dialkyl ethers include dimethyl ether, diethylether, di-n-propyl ether, diisopropyl ether, di-n-butyl ether,diisobutyl ether, di-t-butyl ether, di-n-pentyl ether, diisopentylether, dineopentyl ether, di-n-hexyl ether, di-n-heptyl ether,di-2-ethylhexyl ether, di-n-octyl ether, di-n-nonyl ether, di-n-decylether, and dibenzyl ether.

Specific examples of dicycloalkyl ethers include dicyclopropyl ether,dicyclobutyl ether, dicyclopentyl ether, dicyclohexyl ether,di-2-methylcyclohexyl ether, and di-2-t-butylcyclohexyl ether.

Specific examples of diaryl ethers include diphenyl ether, di-o-tolylether, di-m-tolyl ether, and di-p-tolyl ether.

Specific examples of mixed dihydrocarbyl ethers include n-butyl methylether, isobutyl methyl ether, sec-butyl methyl ether, t-butyl methylether, n-butyl ethyl ether, isobutyl ethyl ether, sec-butyl ethyl ether,t-butyl ethyl ether, t-amyl methyl ether, t-amyl ethyl ether, phenylmethyl ether (also called anisole), phenyl ethyl ether, phenyl n-propylether, phenyl isopropyl ether, phenyl n-butyl ether, phenyl isobutylether, phenyl n-octyl ether, p-tolyl ethyl ether, p-tolyl n-propylether, p-tolyl isopropyl ether, p-tolyl n-butyl ether, p-tolyl isobutylether, p-tolyl t-butyl ether, p-tolyl n-octyl ether, benzyl n-ethylether, benzyl n-propyl ether, benzyl isopropyl ether, benzyl n-butylether, benzyl isobutyl ether, benzyl t-butyl ether, and benzyl n-octylether.

In one or more embodiments, one or both of the hydrocarbyl groups (R) inthe dihydrocarbyl ether may contain one or more additional etherlinkages (i.e., C—O—C). These ether compounds may be referred to aspolyethers. Specific examples of polyethers include glyme ethers such asethylene glycol dimethyl ether (also called monoglyme), ethylene glycoldiethyl ether, diethylene glycol dimethyl ether (also called diglyme),diethylene glycol diethyl ether, diethylene glycol di-n-butyl ether,triethylene glycol dimethyl ether (also called triglyme), triethyleneglycol diethyl ether, tetraethylene glycol dimethyl ether (also calledtetraglyme), and tetraethylene glycol diethyl ether.

In one or more embodiments, suitable amines include those compoundsrepresented by the formula NR₃, where each R, which may be the same ordifferent, is a hydrocarbyl group or substituted hydrocarbyl group, orwhere two or more R groups combine to form a divalent or trivalentorganic group. The hydrocarbyl group may contain heteroatoms such as,but not limited to, nitrogen, oxygen, silicon, tin, sulfur, boron, andphosphorous atoms. Suitable types of hydrocarbyl groups or substitutedhydrocarbyl groups include, but are not limited to, alkyl, cycloalkyl,substituted cycloalkyl, alkenyl, cycloalkenyl, aryl, substituted arylgroups, and heterocyclic groups. Specific examples of hydrocarbyl groupsinclude those provided above for the dihydrocarbyl ether compounds. Incertain embodiments, suitable amines include those compounds where thenitrogen atom of the amine has three bonds to carbon atoms. Specificallycontemplated are those amines where the nitrogen is singly bonded tothree carbon atoms (e.g. trihydrocarbylamines). Also specificallycontemplated are those amines where the nitrogen is singly bonded to acarbon atom and doubly bonded to a second carbon atom (e.g. aromaticamines such as pyridine).

In one or more embodiments, the amines are tertiary amines. In one ormore embodiments, the tertiary amines may include one or more acyclicsubstituents. In other embodiments, the tertiary amines may include oneor more cyclic, non-aromatic substituents. In yet other embodiments, thetertiary amines may include one or more aromatic substituents. Inparticular embodiments, the tertiary amines are devoid of aromaticsubstituents bonded directly to the nitrogen atom of the tertiary amine.In one or more embodiments, the tertiary amines are cyclic non-aromaticamines, where the nitrogen atom of the tertiary amine is a member of anon-aromatic ring. In other embodiments, the tertiary amines arearomatic amines, where the nitrogen atom of the tertiary amine is amember of an aromatic ring. In one or more embodiments, the tertiaryamines are monodentate compounds, which refers to the presence of onlyone lone pair of electrons that are capable of binding or coordinatingto the nickel metal of the nickel-containing compound.

Specific examples of tertiary amines that include acyclic substituentsinclude trimethylamine, triethylamine, tri-n-propylamine,triisopropylamine, tri-n-butylamine, triisobutylamine,tri-sec-butylamine, tripentylamine, triisopentylamine, tri-n-hexylamine,trioctylamine, trioctylamine, tricetylamine, tridodecylamine,triheptylamine, tri-iso-heptylamine, trinonylamine,N-methyl-N,N-dioctylamine, N,N-dimethyl-N-ethylamine,N-methyl-N-ethyl-N-propylamine, N,N-dimethyl-N-hexylamine,tri-isoamylamine, triamylamine.

Specific examples of tertiary amines that include cyclic, non-aromaticsubstituents include tricyclopentylamine, tricyclohexylamine, andtricyclooctylamine.

Specific examples of tertiary amines that include an aromaticsubstituent include N,N-dimethyl-1-naphthylamine, N,N-dimethylaniline,N,N-diethylaniline, N,N-dimethylbenzylamine, triphenyl amine, andtribenzylamine.

Specific examples of cyclic, non-aromatic amines includeN-methylpyrrolidine, 1,2-dimethylpyrrolidine, 1,3-dimethylpyrrolidine,1,2,5-trimethylpyrrolidine, 2-methyl-2-pyrazoline, 1-methyl-2H-pyrrole,2H-pyrrole, 1-methylpyrrole, 2,4-dimethyl-1-methylpyrrole,2,5-dimethyl-1-methylpyrrole, N-methylpyrrole, 1,2,5-trimethylpyrrole,3-pyrroline, 2-pyrroline, 2-methyl-1-pyrroline, 2-imidazoline,N-ethylpiperidine, 1-ethylpiperidine, N-cyclohexyl-N,N-dimethylamine,quinuclidine, 3-(biphenyl-4-yl)quinuclidine, and 1-methyl-carbozole.

Specific examples of aromatic amines include pyridine, methylpyridine,2,6-dimethylpyridine, 2-methylpyridine, 3-methylpyridine,4-methylpyridine, dimethylpyridine, trimethylpyridine, ethylpyridine,2-ethylpyridine, 3-ethylpyridine, 4-ethylpyridine, 2,4-diethylpyridine,2,6-diethylpyridine, 3,4-diethylpyridine, 2,3-, imethylpyridine,2,4-dimethylpyridine, 2,5-dimethylpyridine, 3,4-dimethylpyridine,3,5-dimethylpyridine, triethylpyridine, 1,4,5-triethylpyridine,2,4,5-triethylpyridine, 2,3,4-trimethylpyridine,2,3,5-trimethylpyridine, 2,3,6-trimethylpyridine,2,4,6-trimethylpyridine, propylpyridine, 3-methyl-4-propyl-pyridine,butylpyridine, 4-(1-butylpentyl)pyridine, 4-tert-butylpyridine,phenylpyridine, 3-methyl-2-phenylpyridine, diphenylpyridine,2-phenylpyridine, benzylpyridine, 4-pyrrolidinopyridine,1-methyl-4-phenylpyridine, 2-(1-ethylpropyl)pyridine,2,6-dimethyl-4-ethylpyridine, 3-ethyl-4-methylpyridine,3,5-dimethyl-2-ethylpyridine, 2,3,4,5-tetramethylpyridine, pyrazine,pyridazine, pyrimidine, 4-methylpyrimidine, 1,2,3-triazole,1,3,5-triazine, quinoline, 2-ethylquinoline, 3-ethylquinoline,4-ethylquinoline, 2-methylquinoline, 3-methylquinoline,4-methylquinoline, 5-methylquinoline, 6-methylquinoline,8-methylquinoline, 2,4-dimethylquinoline, 4,6-dimethylquinoline,4,7-dimethylquinoline, 5,8-dimethylquinoline, 6,8-dimethylquinoline,2,4,7-trimethylquinoline, isoquinoline, 4-ethyl-isoquinoline,1-ethylisoquinoline, 3-ethylisoquinoline, 4-methyl-2-phenylimidazole,2-(4-methylphenyl)indolizine, indolizine, quinoxaline,2-amino-8-methyl-quinoxaline, 1-methylindole, 1,8-naphthyridine,cinnoline, quinazoline, pteridine, acridine, phenazine,1-methylpyrazole, 1,3-dimethylpyrazole, 1,3,4-trimethylpyrazole,3,5-dimethyl-1-phenylpyrazole, and 3,4-dimethyl-1-phenylpyrazole.

In one or more embodiments, the amount of the modulating Lewis baseintroduced directly and individually to the monomer to be polymerizedmay depend upon the type of the modulating Lewis base employed. In oneor more embodiments, where a dihydrocarbyl ether is employed as themodulating Lewis base, the amount of the dihydrocarbyl ether employedmay be represented by the molar ratio of the dihydrocarbyl ether to thenickel-containing compound (ether/Ni). In one or more embodiments, theether/Ni molar ratio is from about 10:1 to about 80:1, in otherembodiments from about 20:1 to about 70:1, in other embodiments fromabout 30:1 to about 55:1, and in other embodiments from about 35:1 toabout 45:1.

In one or more embodiments, where an amine is employed as the modulatingLewis base, the amount of the amine employed may be represented by themolar ratio of the amine to the nickel-containing compound (amine/Ni).In one or more embodiments, the amine/Ni molar ratio is from about 0.1:1to about 2.0:1, in other embodiments from about 0.3:1 to about 1.6:1, inother embodiments from about 0.5:1 to about 1.4:1, and in otherembodiments from about 0.7:1 to about 1.2:1.

In one or more embodiments, a solvent may be employed as a carrier toeither dissolve or suspend the catalyst, catalyst ingredients, and/orthe modulating Lewis base in order to facilitate the delivery of thesame to the polymerization system. In other embodiments, monomer can beused as the carrier. In yet other embodiments, the catalyst ingredientsor modulating Lewis base can be introduced in their neat state withoutany solvent.

In one or more embodiments, suitable solvents include those organiccompounds that will not undergo polymerization or incorporation intopropagating polymer chains during the polymerization of monomer in thepresence of the catalyst. In one or more embodiments, these organicspecies are liquid at ambient temperature and pressure. In one or moreembodiments, these organic solvents are inert to the catalyst. Exemplaryorganic solvents include hydrocarbons with a low or relatively lowboiling point such as aromatic hydrocarbons, aliphatic hydrocarbons, andcycloaliphatic hydrocarbons. Non-limiting examples of aromatichydrocarbons include benzene, toluene, xylenes, ethylbenzene,diethylbenzene, and mesitylene. Non-limiting examples of aliphatichydrocarbons include n-pentane, n-hexane, n-heptane, n-octane, n-nonane,n-decane, isopentane, isohexanes, isopentanes, isooctanes,2,2-dimethylbutane, petroleum ether, kerosene, and petroleum spirits.And, non-limiting examples of cycloaliphatic hydrocarbons includecyclopentane, cyclohexane, methylcyclopentane, and methylcyclohexane.Mixtures of the above hydrocarbons may also be used. As is known in theart, aliphatic and cycloaliphatic hydrocarbons may be desirably employedfor environmental reasons. The low-boiling hydrocarbon solvents aretypically separated from the polymer upon completion of thepolymerization.

Other examples of organic solvents include high-boiling hydrocarbons ofhigh molecular weights, including hydrocarbon oils that are commonlyused to oil-extend polymers. Examples of these oils include paraffinicoils, aromatic oils, naphthenic oils, vegetable oils other than castoroils, and low PCA oils including MES, TDAE, SRAE, heavy naphthenic oils.Since these hydrocarbons are non-volatile, they typically do not requireseparation and remain incorporated in the polymer.

The production of polymer according to this invention can beaccomplished by polymerizing conjugated diene monomer in the presence ofa catalytically effective amount of the active catalyst. Theintroduction of the catalyst, the conjugated diene monomer, themodulating Lewis base, and any solvent, if employed, forms apolymerization mixture in which a polymer is formed. The amount of thecatalyst to be employed may depend on the interplay of various factorssuch as the type of catalyst employed, the purity of the ingredients,the polymerization temperature, the polymerization rate and conversiondesired, the molecular weight desired, and many other factors.Accordingly, a specific catalyst amount cannot be definitively set forthexcept to say that catalytically effective amounts of the catalyst maybe used.

In one or more embodiments, the amount of the nickel-containing compoundused can be varied from about 0.001 to about 0.100 mmol, in otherembodiments from about 0.005 to about 0.050 mmol, and in still otherembodiments from about 0.010 to about 0.030 mmol per 100 gram ofmonomer.

In one or more embodiments, the polymerization of conjugated dienemonomer according to this invention may be conducted in a bulkpolymerization system that includes substantially no solvent or aminimal amount of solvent. Those skilled in the art will appreciate thebenefits of bulk polymerization processes (i.e., processes where monomeracts as the solvent), and therefore the polymerization system includesless solvent than will deleteriously impact the benefits sought byconducting bulk polymerization. In one or more embodiments, the solventcontent of the polymerization mixture may be less than about 20% byweight, in other embodiments less than about 10% by weight, and in stillother embodiments less than about 5% by weight based on the total weightof the polymerization mixture. In another embodiment, the polymerizationmixture contains no solvents other than those that are inherent to theraw materials employed. In still another embodiment, the polymerizationmixture is substantially devoid of solvent, which refers to the absenceof that amount of solvent that would otherwise have an appreciableimpact on the polymerization process. Polymerization systems that aresubstantially devoid of solvent may be referred to as includingsubstantially no solvent. In particular embodiments, the polymerizationmixture is devoid of solvent.

The polymerization may be conducted in any conventional polymerizationvessels known in the art. In one or more embodiments, the polymerizationcan be conducted in a conventional stirred-tank reactor, which mayoptionally be used in conjunction with other types of reactors, such asextruders or devolatilizers. Examples of useful bulk polymerizationprocesses are disclosed in U.S. Pat. No. 7,351,776, which isincorporated herein by reference.

In one or more embodiments, all of the ingredients used for thepolymerization can be combined within a single vessel (e.g., aconventional stirred-tank reactor), and all steps of the polymerizationprocess can be conducted within this vessel. In other embodiments, twoor more of the ingredients can be pre-combined in one vessel and thentransferred to another vessel where the polymerization of monomer (or atleast a major portion thereof) may be conducted.

The polymerization can be carried out as a batch process, a continuousprocess, or a semi-continuous process. In the semi-continuous process,the monomer is intermittently charged as needed to replace that monomeralready polymerized. In one or more embodiments, the conditions underwhich the polymerization proceeds may be controlled to maintain thetemperature of the polymerization mixture within a range from about −10°C. to about 130° C., in other embodiments from about 0° C. to about 100°C., and in other embodiments from about 10° C. to about 80° C. Inparticular embodiments, the peak temperature of the polymerizationmixture during the course of the polymerization is greater than 34° C.,in other embodiments greater than 40° C., and in other embodimentsgreater than 45° C.

In one or more embodiments, the heat of polymerization may be removed byexternal cooling by a thermally controlled reactor jacket, internalcooling by evaporation and condensation of the monomer through the useof a reflux condenser connected to the reactor, or a combination of thetwo methods. Also, the polymerization conditions may be controlled toconduct the polymerization under a pressure of from about 0.1 atmosphereto about 50 atmospheres, in other embodiments from about 0.5 atmosphereto about 20 atmosphere, and in other embodiments from about 1 atmosphereto about 10 atmospheres. In one or more embodiments, the pressures atwhich the polymerization may be carried out include those that ensurethat the majority of the monomer is in the liquid phase. In these orother embodiments, the polymerization mixture may be maintained underanaerobic conditions.

In one or more embodiments, the bulk polymerization process of thisinvention is maintained at a relatively low monomer conversion in orderto avoid polymer gel formation. In one or more embodiments, the monomerconversion is maintained at less than 30%, in other embodiments lessthan 20%, in other embodiments less than 15%, and in other embodimentsless than 12%. In one or more embodiments, the monomer concentrationwithin the polymerization vessel is maintained at greater than 70% byweight, in other embodiments greater than 80% by weight, in otherembodiments greater than 85% by weight, and in other embodiments greaterthan 88% by weight based on the total weight of the polymerizationmixture within the polymerization vessel.

Once a desired monomer conversion has been achieved, a quenching agentcan be added to the polymerization mixture in order to inactivate anyreactive polymer chains and the catalyst or catalyst ingredients. Thequenching agent may be a protic compound, which includes, but is notlimited to, an alcohol, a carboxylic acid, an inorganic acid, water, ora mixture thereof. In particular embodiments, the quenching agentincludes a polyhydroxy compound as disclosed in U.S. Pat. Publ. No.2009/0043055, which is incorporated herein by reference. An antioxidantsuch as 2,6-di-t-butyl-4-methylphenol may be added along with, before,or after the addition of the quenching agent. The amount of theantioxidant employed may be in the range of about 0.2% to about 1% byweight of the polymer product. The quenching agent and the antioxidantmay be added as neat materials or, if necessary, dissolved in ahydrocarbon solvent or conjugated diene monomer prior to being added tothe polymerization mixture. Additionally, the polymer product can be oilextended by adding an oil to the polymer, which may be in the form of apolymer cement or polymer dissolved or suspended in monomer. Practice ofthe present invention does not limit the amount of oil that may beadded, and therefore conventional amounts may be added (e.g., 5-50 phr).Useful oils or extenders that may be employed include, but are notlimited to, aromatic oils, paraffinic oils, naphthenic oils, vegetableoils other than castor oils, low PCA oils including MES, TDAE, and SRAE,and heavy naphthenic oils.

Once the polymerization mixture has been quenched, the variousconstituents of the polymerization mixture may be recovered. In one ormore embodiments, the unreacted monomer can be recovered from thepolymerization mixture. For example, the monomer can be distilled fromthe polymerization mixture by using techniques known in the art. In oneor more embodiments, a devolatilizer may be employed to remove themonomer from the polymerization mixture. Once the monomer has beenremoved from the polymerization mixture, the monomer may be purified,stored, and/or recycled back to the polymerization process.

The polymer product may be recovered from the polymerization mixture byusing techniques known in the art. In one or more embodiments,desolventization and drying techniques may be used. For instance, thepolymer can be recovered by passing the polymerization mixture through aheated screw apparatus, such as a desolventizing extruder, in which thevolatile substances are removed by evaporation at appropriatetemperatures (e.g., about 100° C. to about 170° C.) and underatmospheric or sub-atmospheric pressure. This treatment serves to removeunreacted monomer as well as any low-boiling solvent. Alternatively, thepolymer can also be recovered by subjecting the polymerization mixtureto steam desolventization, followed by drying the resulting polymercrumbs in a hot air tunnel. The polymer can also be recovered bydirectly drying the polymerization mixture on a drum dryer.

In one or more embodiments, the polymers prepared according to thisinvention may contain unsaturation. In these or other embodiments, thepolymers are vulcanizable. In one or more embodiments, the polymers canhave a glass transition temperature (T_(g)) that is less than 0° C., inother embodiments less than −20° C., and in other embodiments less than−30° C. In one embodiment, these polymers may exhibit a single glasstransition temperature. In particular embodiments, the polymers may behydrogenated or partially hydrogenated.

In one or more embodiments, the polymers of this invention may becis-1,4-polydienes having a cis-1,4-linkage content that is greater than97%, in other embodiments greater than 97.5%, in other embodimentsgreater than 98.0%, and in other embodiments greater than 98.5%, wherethe percentages are based upon the number of diene mer units adoptingthe cis-1,4-linkage versus the total number of diene mer units. Also,these polymers may have a 1,2-linkage content that is less than about1.0%, in other embodiments less than 0.8%, in other embodiments lessthan 0.7%, and in other embodiments less than 0.6%, where thepercentages are based upon the number of diene mer units adopting the1,2-linkage versus the total number of diene mer units. The balance ofthe diene mer units may adopt the trans-1,4-linkage. The cis-1,4-, 1,2-,and trans-1,4-linkage contents can be determined by infraredspectroscopy.

In one or more embodiments, the number average molecular weight (M_(n))of these polymers may be from about 1,000 to about 1,000,000, in otherembodiments from about 5,000 to about 200,000, in other embodiments fromabout 25,000 to about 150,000, and in other embodiments from about50,000 to about 120,000, as determined by using gel permeationchromatography (GPC) calibrated with polystyrene standards andMark-Houwink constants for the polymer in question.

In one or more embodiments, the molecular weight distribution orpolydispersity (M_(w)/M_(n)) of these polymers may be less than 3.0, inother embodiments less than 2.9, in other embodiments less than 2.6, inother embodiments less than 2.5, in other embodiments less than 2.3, inother embodiments less than 2.1, in other embodiments less than 2.0, andin other embodiments less than 1.9.

In one or more embodiments, the Mooney viscosity (ML₁₊₄@ 100° C.) of thepolymers may be less than 60, in other embodiments less than 50, inother embodiments less than 40, and in other embodiments less than 25.

In one or more embodiments, the gel content of the polymers may be lessthan 20% by weight, in other embodiments less than 10% by weight, inother embodiments less than 7% by weight, in other embodiments less than5% by weight, in other embodiments less than 3% by weight, and in otherembodiments less than 2% by weight, as determined by measuring, at roomtemperature, the amount of toluene-insoluble material in the polymers.

The polymers of this invention are particularly useful in preparingrubber compositions that can be used to manufacture tire components.Rubber compounding techniques and the additives employed therein aregenerally disclosed in The Compounding and Vulcanization of Rubber, inRubber Technology (2^(nd) Ed. 1973).

The rubber compositions can be prepared by using the polymers of thisinvention alone or together with other elastomers (i.e., polymers thatcan be vulcanized to form compositions possessing rubbery or elastomericproperties). Other elastomers that may be used include natural andsynthetic rubbers. The synthetic rubbers typically derive from thepolymerization of conjugated diene monomers, the copolymerization ofconjugated diene monomers with other monomers such as vinyl-substitutedaromatic monomers, or the copolymerization of ethylene with one or moreα-olefins and optionally one or more diene monomers.

Exemplary elastomers include natural rubber, synthetic polyisoprene,polybutadiene, polyisobutylene-co-isoprene, neoprene,poly(ethylene-co-propylene), poly(styrene-co-butadiene),poly(styrene-co-isoprene), poly(styrene-co-isoprene-co-butadiene),poly(isoprene-co-butadiene), poly(ethylene-co-propylene-co-diene),polysulfide rubber, acrylic rubber, urethane rubber, silicone rubber,epichlorohydrin rubber, and mixtures thereof. These elastomers can havea myriad of macromolecular structures including linear, branched, andstar-shaped structures.

The rubber compositions may include fillers such as inorganic andorganic fillers. Examples of organic fillers include carbon black andstarch. Examples of inorganic fillers include silica, aluminumhydroxide, magnesium hydroxide, mica, talc (hydrated magnesiumsilicate), and clays (hydrated aluminum silicates). Carbon blacks andsilicas are the most common fillers used in manufacturing tires. Incertain embodiments, a mixture of different fillers may beadvantageously employed.

In one or more embodiments, carbon blacks include furnace blacks,channel blacks, and lamp blacks. More specific examples of carbon blacksinclude super abrasion furnace blacks, intermediate super abrasionfurnace blacks, high abrasion furnace blacks, fast extrusion furnaceblacks, fine furnace blacks, semi-reinforcing furnace blacks, mediumprocessing channel blacks, hard processing channel blacks, conductingchannel blacks, and acetylene blacks.

In particular embodiments, the carbon blacks may have a surface area(EMSA) of at least 20 m²/g and in other embodiments at least 35 m²/g;surface area values can be determined by ASTM D-1765 using thecetyltrimethylammonium bromide (CTAB) technique. The carbon blacks maybe in a pelletized form or an unpelletized flocculent form. Thepreferred form of carbon black may depend upon the type of mixingequipment used to mix the rubber compound.

The amount of carbon black employed in the rubber compositions can be upto about 50 parts by weight per 100 parts by weight of rubber (phr),with about 5 to about 40 phr being typical.

Some commercially available silicas which may be used include Hi-Sil™215, Hi-Sil™ 233, and Hi-Sil™ 190 (PPG Industries, Inc.; Pittsburgh,Pa.). Other suppliers of commercially available silica include GraceDavison (Baltimore, Md.), Degussa Corp. (Parsippany, N.J.), RhodiaSilica Systems (Cranbury, N.J.), and J.M. Huber Corp. (Edison, N.J.).

In one or more embodiments, silicas may be characterized by theirsurface areas, which give a measure of their reinforcing character. TheBrunauer, Emmet and Teller (“BET”) method (described in J. Am. Chem.Soc., vol. 60, p. 309 et seq.) is a recognized method for determiningthe surface area. The BET surface area of silica is generally less than450 m²/g. Useful ranges of surface area include from about 32 to about400 m²/g, about 100 to about 250 m²/g, and about 150 to about 220 m²/g.

The pH's of the silicas are generally from about 5 to about 7 orslightly over 7, or in other embodiments from about 5.5 to about 6.8.

In one or more embodiments, where silica is employed as a filler (aloneor in combination with other fillers), a coupling agent and/or ashielding agent may be added to the rubber compositions during mixing inorder to enhance the interaction of silica with the elastomers. Usefulcoupling agents and shielding agents are disclosed in U.S. Pat. Nos.3,842,111, 3,873,489, 3,978,103, 3,997,581, 4,002,594, 5,580,919,5,583,245, 5,663,396, 5,674,932, 5,684,171, 5,684,172 5,696,197,6,608,145, 6,667,362, 6,579,949, 6,590,017, 6,525,118, 6,342,552, and6,683,135, which are incorporated herein by reference.

The amount of silica employed in the rubber compositions can be fromabout 1 to about 100 phr or in other embodiments from about 5 to about80 phr. The useful upper range is limited by the high viscosity impartedby silicas. When silica is used together with carbon black, the amountof silica can be decreased to as low as about 1 phr; as the amount ofsilica is decreased, lesser amounts of coupling agents and shieldingagents can be employed. Generally, the amounts of coupling agents andshielding agents range from about 4% to about 20% based on the weight ofsilica used.

A multitude of rubber curing agents (also called vulcanizing agents) maybe employed, including sulfur or peroxide-based curing systems. Curingagents are described in Kirk-Othmer, ENCYCLOPEDIA OF CHEMICALTECHNOLOGY, Vol. 20, pgs. 365-468, (3^(rd) Ed. 1982), particularlyVulcanization Agents and Auxiliary Materials, pgs. 390-402, and A. Y.Coran, Vulcanization, ENCYCLOPEDIA OF POLYMER SCIENCE AND ENGINEERING,(2^(nd) Ed. 1989), which are incorporated herein by reference.Vulcanizing agents may be used alone or in combination.

Other ingredients that are typically employed in rubber compounding mayalso be added to the rubber compositions. These include accelerators,accelerator activators, oils, plasticizer, waxes, scorch inhibitingagents, processing aids, zinc oxide, tackifying resins, reinforcingresins, fatty acids such as stearic acid, peptizers, and antidegradantssuch as antioxidants and antiozonants. In particular embodiments, theoils that are employed include those conventionally used as extenderoils, which are described above.

All ingredients of the rubber compositions can be mixed with standardmixing equipment such as Banbury or Brabender mixers, extruders,kneaders, and two-rolled mills. In one or more embodiments, theingredients are mixed in two or more stages. In the first stage (oftenreferred to as the masterbatch mixing stage), a so-called masterbatch,which typically includes the rubber component and filler, is prepared.To prevent premature vulcanization (also known as scorch), themasterbatch may exclude vulcanizing agents. The masterbatch may be mixedat a starting temperature of from about 25° C. to about 125° C. with adischarge temperature of about 135° C. to about 180° C. Once themasterbatch is prepared, the vulcanizing agents may be introduced andmixed into the masterbatch in a final mixing stage, which is typicallyconducted at relatively low temperatures so as to reduce the chances ofpremature vulcanization. Optionally, additional mixing stages, sometimescalled remills, can be employed between the masterbatch mixing stage andthe final mixing stage. One or more remill stages are often employedwhere the rubber composition includes silica as the filler. Variousingredients including the polymers of this invention can be added duringthese remills.

The mixing procedures and conditions particularly applicable tosilica-filled tire formulations are described in U.S. Pat. Nos.5,227,425, 5,719,207, and 5,717,022, as well as European Patent No.890,606, all of which are incorporated herein by reference. In oneembodiment, the initial masterbatch is prepared by including the polymerand silica in the substantial absence of coupling agents and shieldingagents.

The rubber compositions prepared from the polymers of this invention areparticularly useful for forming tire components such as treads,subtreads, sidewalls, body ply skims, bead filler, and the like. In oneor more embodiments, these tread or sidewall formulations may includefrom about 10% to about 100% by weight, in other embodiments from about35% to about 90% by weight, and in other embodiments from about 50% toabout 80% by weight of the polymer of this invention based on the totalweight of the rubber within the formulation.

Where the rubber compositions are employed in the manufacture of tires,these compositions can be processed into tire components according toordinary tire manufacturing techniques including standard rubbershaping, molding and curing techniques. Typically, vulcanization iseffected by heating the vulcanizable composition in a mold; e.g., it maybe heated to about 140° C. to about 180° C. Cured or crosslinked rubbercompositions may be referred to as vulcanizates, which generally containthree-dimensional polymeric networks that are thermoset. The otheringredients, such as fillers and processing aids, may be evenlydispersed throughout the crosslinked network. Pneumatic tires can bemade as discussed in U.S. Pat. Nos. 5,866,171, 5,876,527, 5,931,211, and5,971,046, which are incorporated herein by reference.

In order to demonstrate the practice of the present invention, thefollowing examples have been prepared and tested. The examples shouldnot, however, be viewed as limiting the scope of the invention. Theclaims will serve to define the invention.

EXAMPLES Example 1

The polymerization reactor consisted of a one-gallon stainless cylinderequipped with a mechanical agitator (shaft and blades) capable of mixinghigh viscosity polymer cement. The top of the reactor was connected to areflux condenser system for conveying, condensing, and recycling the1,3-butadiene vapor developed inside the reactor throughout the durationof the polymerization. The reactor was also equipped with a coolingjacket chilled by cold water. The heat of polymerization was dissipatedpartly by internal cooling through the use of the reflux condensersystem, and partly by external cooling through heat transfer to thecooling jacket.

The reactor was thoroughly purged with a stream of dry nitrogen, whichwas then replaced with 1,3-butadiene vapor by charging 100 g of dry1,3-butadiene monomer to the reactor, heating the reactor to 65° C., andthen venting the 1,3-butadiene vapor from the top of the refluxcondenser system until no liquid 1,3-butadiene remained in the reactor.Cooling water was applied to the reflux condenser and the reactorjacket, and 1302 g of 1,3-butadiene monomer was charged into thereactor. After the monomer was thermostated at 32° C., 6.2 mL of 1.0 Mtriisobutylaluminum (TIBA) in hexane and 4.6 mL of 0.054 M nickel (II)neodecanoate borate (NiOB) in hexane was charged into the reactor. Afterstirring the solution for 5 minutes, 8.9 mL of 1.0 M borontrifluoride-hexanol-complex (BF₃.hexanol) was charged into the reactorand initiated polymerization. Within 1 minute following the addition ofBF₃.hexanol, 1.7 mL (9.9 mmol) of di-n-butyl ether (Bu₂O) was charged tothe reactor. After 5.0 minutes from its commencement, the polymerizationwas terminated by diluting the polymerization mixture with 6.0 mLisopropanol dissolved in 1360 g of hexane and dropping the batch into 3gallons of isopropanol containing 5 g of2,6-di-tert-butyl-4-methylphenol. The coagulated polymer was drum-dried.

The yield of the polymer was 179.6 g (13.8% conversion), and thepolymerization rate was calculated to be 2.8% conversion per minute. TheMooney viscosity (ML₁₊₄) of the polymer was determined to be 21.4 at100° C. by using a Monsanto Mooney viscometer with a large rotor, aone-minute warm-up time, and a four minute running time. As determinedby gel permeation chromatography (GPC), the polymer had a number averagemolecular weight (M_(n)) of 91,000, a weight average molecular weight(M_(w)) of 229,000, and a molecular weight distribution (M_(w)/M_(n)) of2.5. The infrared spectroscopic analysis of the polymer indicatedacis-1,4-linkage content of 97.4%, a trans-1,4-linkage content of 2.1%,and a 1,2-linkage content of 0.5%. The gel content of the polymer wasdetermined by measuring, at room temperature, the amount oftoluene-insoluble material in the polymer sample, and the polymer wasdetermined to be gel free.

Example 2

The same procedure used in Example 1 was used except that 7.0 mL of 1.0M TIBA in hexane was used and 0.62 mL 0.4 M pyridine was added in lieuof Bu₂O within 1 minute following the addition of BF₃.hexanol. After 8.0minutes from its commencement, the polymerization was terminated bydiluting the polymerization mixture with 6.0 mL isopropanol dissolved in1360 g of hexane and dropping the batch into 3 gallons of isopropanolcontaining 5 g of 2,6-di-tert-butyl-4-methylphenol. The coagulatedpolymer was drum-dried.

The yield of the polymer was 190.2 g (14.6% conversion), and thepolymerization rate was calculated to be 1.8% conversion per minute. Theresulting polymer had the following properties: ML₁₊₄=23.7, Mn=95,000,Mw=208,000, Mw/Mn=2.2, cis-1,4-linkage content=96.9%, trans-1,4-linkagecontent=2.6%, and 1,2-linkage content=0.5%. The polymer was determinedto be gel free.

Example 3

The same procedure used in Example 1 was used except that 5.9 mL of 1.0M TIBA in hexane was used and the monomer was thermostated at 12° C.,and 1.7 mL (9.9 mmol) of Bu₂O was added within 1 minute following theaddition of BF₃. hexanol. After 5.0 minutes from commencement of thepolymerization, the temperature increased to 19° C., and thepolymerization was terminated by diluting the polymerization mixturewith 6.0 mL isopropanol dissolved in 1360 g of hexane. The batch wasdropped into 3 gallons of isopropanol containing 5 g of2,6-di-tert-butyl-4-methylphenol. The coagulated polymer was drum-dried.

The yield of the polymer was 134.0 g (10.3% conversion), and thepolymerization rate was calculated to be 2.1% conversion per minute. Theresulting polymer had the following properties: ML₁₊₄=36.3, Mn=113,000,Mw=265,000, Mw/Mn=2.3, cis-1,4-linkage content=97.7%, trans-1,4-linkagecontent=1.8%, and 1,2-linkage content=0.5%. The polymer was determinedto be gel free.

Example 4

The same procedure used in Example 3 was used except that 7.4 mL of 1.0M TIBA in hexane was used and 0.62 mL 0.4 M pyridine was added in lieuof Bu₂O within 1 minute following the addition of BF₃.hexanol. After10.6 minutes from commencement of the polymerization, the temperatureincreased to 17° C., and the polymerization was terminated by dilutingthe polymerization mixture with 6.0 mL isopropanol dissolved in 1360 gof hexane and dropping the batch into 3 gallons of isopropanolcontaining 5 g of 2,6-di-tert-butyl-4-methylphenol. The coagulatedpolymer was drum-dried.

The yield of the polymer was 170.9 g (13.1% conversion), and thepolymerization rate was calculated to be 1.2% conversion per minute. Theresulting polymer had the following properties: ML₁₊₄=30.3, Mn=108,000,Mw=226,000, Mw/Mn=2.1, cis-1,4-linkage content=97.3%, trans-1,4-linkagecontent=2.2%, and 1,2-linkage content=0.5%. The polymer was determinedto be gel free.

Example 5 (Comparative Example)

The same procedure used in Example 1 was except that 7.4 mL of 1.0 MTIBA in hexane was used and the polymerization was conducted without theaddition of a modulating Lewis base such as di-n-butyl ether or pyridineto the monomer. After 4.0 minutes from commencement of thepolymerization, the temperature increased to 34° C., and gel formationrapidly occurred on the walls of the reactor and on the shaft of theagitator. Upon gel formation, the polymerization was immediatelyterminated by diluting the polymerization mixture with 6.0 mLisopropanol dissolved in 1360 g of hexane. Most of the polymer gelremained in the reactor while the polymer was isolated by dropping thebatch into 3 gallons of isopropanol containing 5 g of2,6-di-tert-butyl-4-methylphenol. The coagulated polymer was drum-dried.

The yield of the isolated polymer was 209.7 g (16.2% conversion)although the actual yield was much higher due to the polymer gelremaining in the reactor. The reactor had to be cleaned by disassemblingthe reactor and removing the polymer gel from the reactor walls andagitator. The isolated polymer had the following properties: ML₁₊₄=tohigh to measure, Mn=178,000, Mw=548,000, Mw/Mn=3.1, cis-1,4-linkagecontent=98.1%, trans-1,4-linkage content=1.4%, and 1,2-linkagecontent=0.5%. Although the isolated polymer was determined to be gelfree, a significant amount of polymer gel remained inside the reactor,as mentioned above.

A comparison of these results with those of Examples 1 and 2 shows thatuseful polymerizations cannot be achieved at higher temperatures in theabsence of a modulating Lewis base such as di-n-butyl ether or pyridine.

Example 6 (Comparative Example)

The same procedure generally used in Example 1 was used except that 6.2mL of 1.0 M TIBA in hexane was used, 24.7 mL of 0.4 M Bu₂O in hexane wasadded within 1 minute following the addition of BF₃.hexanol, and thepolymerization was allowed to continue to greater conversion. After 6.5minutes from commencement of the polymerization, gel formation occurredon the walls of the reactor and on the shaft of the agitator whilefoaming of the polymerization mixture crept toward the condenser. Uponfoaming, the polymerization was terminated by diluting thepolymerization mixture with 6.0 mL isopropanol dissolved in 1360 g ofhexane. The polymer gel remained in the reactor while the polymer wasisolated by dropping the batch into 3 gallons of isopropanol containing5 g of 2,6-di-tert-butyl-4-methylphenol. The coagulated polymer wasdrum-dried.

The yield of the isolated polymer was 192.9 g (14.8% conversion)although the actual yield was higher due to the polymer gel remaining inthe reactor. The reactor had to be cleaned by disassembling the reactorand removing the polymer gel from the reactor walls and agitator. Theisolated polymer had the following properties: ML₁₊₄=16.8, Mn=84,000,Mw=183,000, Mw/Mn=2.2, cis-1,4-linkage content=97.2%, trans-1,4-linkagecontent=2.2%, and 1,2-linkage content=0.6%. Although the isolatedpolymer was determined to be gel free, a significant amount of polymergel remained inside the reactor, as mentioned above.

A comparison of these results with those of Example 1 shows thecriticality of maintaining relatively low conversions in order toachieve useful polymerizations even where a modulating Lewis base suchas di-n-butyl ether is added to the monomer to be polymerized.

Example 7(Comparative Example)

The same procedure used in Example 6 was used except that 6.2 mL of 1.0M TIBA in hexane was used and 0.62 mL 0.4 M pyridine was added in lieuof Bu₂O within 1 minute following the addition of BF₃.hexanol. After 9.0minutes from commencement of the polymerization, gel formation occurredon the walls of the reactor and on the shaft of the agitator whilefoaming of the polymerization mixture crept toward the condenser. Uponfoaming, the polymerization was terminated by diluting thepolymerization mixture with 6.0 mL isopropanol dissolved in 1360 g ofhexane. The polymer gel remained in the reactor while the polymer wasisolated by dropping the batch into 3 gallons of isopropanol containing5 g of 2,6-di-tert-butyl-4-methylphenol. The coagulated polymer wasdrum-dried.

The yield of the isolated polymer was 281.6 g (21.6% conversion)although the actual yield was much higher due to the polymer gelremaining in the reactor. The reactor had to be cleaned by disassemblingthe reactor and removing the polymer gel from the reactor walls andagitator. The isolated polymer had the following properties: ML₁₊₄=2.0,Mn=52,000, Mw=107,000, Mw/Mn=2.1, cis-1,4-linkage content=96.7%,trans-1,4-linkage content=2.7%, and 1,2-linkage content=0.6%. Althoughthe isolated polymer was determined to be gel free, a significant amountof polymer gel remained inside the reactor, as mentioned above.

A comparison of these results with those of Example 2 shows thecriticality of maintaining relatively low conversions in order toachieve useful polymerizations even where a modulating Lewis base suchas pyridine is added to the monomer to be polymerized.

Example 8 (Comparative Example)

The same procedure used in Example 5 was used except that 6.2 mL of 1.0M TIBA in hexane was used, and 8.9 mL of 1.0 M boron trifluoride dibutyletherate (BF₃.Bu₂O) was used in lieu of BF₃.hexanol. After 28.0 minutesfrom commencement of the polymerization, the polymerization wasterminated by diluting the polymerization mixture with 6.0 mLisopropanol dissolved in 1360 g of hexane and dropping the batch into 3gallons of isopropanol containing 5 g of2,6-di-tert-butyl-4-methylphenol. The coagulated polymer was drum-dried.There was a small amount of gel formation on the walls of the reactorand on the agitator.

The yield of the isolated polymer was 17.5 g (1.3% conversion), and thepolymerization rate was calculated to be 0.05% conversion per minute.The isolated polymer had the following properties: ML₁₊₄=not enoughsample to measure, Mn=35,000, Mw=129,000, Mw/Mn=3.7, cis-1,4-linkagecontent=95.9%, trans-1,4-linkage content=3.3%, and 1,2-linkagecontent=0.8%. Although the isolated polymer was determined to includeonly 0.9% of gel, additional gel remained inside the reactor, asmentioned above.

A comparison of these results with those of Example 1 shows that theaddition of Bu₂O to the polymerization system via the use of BF₃.Bu₂Ocomplex inhibits polymerization. Thus, the direct and separate additionof a modulating Lewis base such as Bu₂O to the polymerization system, asexemplified in Example 1, is critical for achieving usefulpolymerizations at higher temperatures.

Example 9 (Comparative Example)

The same procedure used in Example 8 was used except that 6.2 mL of 1.0M triethylaluminum (TEA) in hexane was used in lieu of TIBA. After 14.0minutes from commencement of the polymerization, the polymerization wasterminated by diluting the polymerization mixture with 6.0 mLisopropanol dissolved in 1360 g of hexane and dropping the batch into 3gallons of isopropanol containing 5 g of2,6-di-tert-butyl-4-methylphenol. During the bulk polymerization, gelformation occurred on the walls of the reactor and on the shaft of theagitator. The reactor had to be cleaned by disassembling the reactor andremoving the polymer gel from the reactor walls and agitator. Thecoagulated polymer was drum-dried.

The yield of the isolated polymer was 209.9 g (16.1% conversion), andthe polymerization rate was calculated to be 1.2% conversion per minute.The isolated polymer had the following properties: ML₁₊₄=48.2,Mn=92,000, Mw=290,000, Mw/Mn=3.2, cis-1,4-linkage content=97.6%,trans-1,4-linkage content=1.5%, and 1,2-linkage content=0.9%. Althoughthe isolated polymer was determined to be gel free, a significant amountof polymer gel remained inside the reactor, as mentioned above.

A comparison of these results with those of Example 8 shows that the useof TEA instead of TIBA allows the bulk polymerization to proceed whenBF₃.Bu₂O is used. However, a comparison of these results with those ofExample 1 shows that the addition of Bu₂O via the BF₃.Bu₂O complex doesnot provide the same benefit as when the Bu₂O is added directly andindividually to the monomer since the polymerization of Example 9resulted in the formation of gel.

Various modifications and alterations that do not depart from the scopeand spirit of this invention will become apparent to those skilled inthe art. This invention is not to be duly limited to the illustrativeembodiments set forth herein.

What is claimed is:
 1. A process for preparing a polydiene, the processcomprising the steps of: (i.) providing conjugated diene monomer; (ii.)charging a nickel-based catalyst system to the conjugated diene monomer;and (iii.) charging a modulating Lewis base to the conjugated dienemonomer, to thereby polymerize the conjugated diene monomer in thepresence of the modulating Lewis base, where said step of charging amodulating Lewis base is separate from said step of charging anickel-based catalyst, and where said steps of providing conjugateddiene monomer, charging a nickel-based catalyst system and charging aLewis base form a polymerization mixture that includes less than 20% byweight of organic solvent based on the total weight of thepolymerization mixture, where said step of charging a nickel-basedcatalyst system to the conjugated diene monomer takes place prior tosaid step of charging a modulating Lewis base to the conjugated dienemonomer, and said step of charging a modulating Lewis base takes placebefore 5% of the conjugated diene monomer is polymerized, or where saidstep of charging a modulating Lewis base to the conjugated diene monomertakes place prior to said step of charging a nickel-based catalystsystem to the conjugated diene monomer, and where the polydiene has acis-1,4-linkage content of at least 97%, a 1,2-linkage content of lessthan 1.0%, a molecular weight distribution of less than 3.0, a Mooneyviscosity (ML₁₊₄@100° C.) of less than 60, and a gel content of lessthan 20% by weight, where the nickel-based catalyst system is thecombination or reaction product of (a) a nickel-containing compound, (b)an alkylating agent, and (c) a fluorine source, and where the molarratio of the alkylating agent to the nickel-containing compound is fromabout 10:1 to about 50:1, and where the ratio of the moles of fluorineatoms in the fluorine source to the moles of nickel atoms in thenickel-containing compound is from about 70:1 to about 130:1.
 2. Theprocess of claim 1, where the nickel-containing compound is selectedfrom the group consisting of nickel carboxylates, nickel carboxylateborates, nickel organophosphates, nickel organophosphonates, nickelorganophosphinates, nickel carbamates, nickel dithiocarbamates, nickelxanthates, nickel β-diketonates, nickel alkoxides or aryloxides, nickelhalides, nickel pseudo-halides, nickel oxyhalides, and organonickelcompounds.
 3. The process of claim 1, where the alkylating agent isdefined by the formula AlR_(n)X_(3-n), where each R independently can bea monovalent organic group that is attached to the aluminum atom via acarbon atom, where each X independently can be a hydrogen atom, ahalogen atom, a carboxylate group, an alkoxide group, or an aryloxidegroup, and where n can be an integer in the range of from 1 to
 3. 4. Theprocess of claim 1, where the fluorine source is selected from the groupconsisting of elemental fluorine, halogen fluorides, hydrogen fluoride,organic fluorides, inorganic fluorides, metallic fluorides,organometallic fluorides, and mixtures thereof.
 5. The process of claim1, where the nickel-containing compound is a nickel carboxylate borate,the alkylating agent is trihydrocarbylaluminum, and the fluorine sourceis an inorganic fluoride.
 6. The process of claim 5, where the inorganicfluoride source is complexed with an alcohol.
 7. The process of claim 1,where the molar ratio of the alkylating agent to the nickel-containingcompound is from about 20:1 to about 40:1, and where the molar ratio ofthe fluorine source to the nickel-containing compound is from about 80:1to about 120:1.
 8. The process of claim 7, where the molar ratio of thealkylating agent to the nickel-containing compound is from about 25:1 toabout 35:1, and where the molar ratio of the fluorine source to thenickel-containing compound is from about 90:1 to about 108:1.
 9. Theprocess of claim 1, where the polymerization mixture includes less than5% by weight of organic solvent.
 10. The process of claim 1, where thetemperature of the polymerization mixture is maintained within a rangefrom about −10° C. to about 130° C.
 11. The process of claim 1, wherethe peak temperature of the polymerization mixture is greater than 34°C.
 12. The process of claim 1, where the polymerization mixture isdevoid of a molecular weight regulator.
 13. The process of claim 1,where the polymerization of the conjugated diene monomer is maintainedat less than 30% conversion.
 14. The process of claim 1, where themodulating Lewis base is a dihydrocarbyl ether or an amine.
 15. Theprocess of claim 14, where the modulating Lewis base is a dihydrocarbylether selected from the group consisting of dialkyl ethers, dicycloalkylethers, diaryl ethers, and mixed dihydrocarbyl ethers.
 16. The processof claim 15, where the nickel-based catalyst system includes anickel-containing compound, and where the molar ratio of thedihydrocarbyl ether to the nickel-containing compound is from about 10:1to about 80:1.
 17. The process of claim 14, where the modulating Lewisbase is a tertiary amine.
 18. The process of claim 17, where thenickel-based catalyst system includes a nickel-containing compound,where the molar ratio of the tertiary amine to the nickel-containingcompound is from about 0.1:1 to about 2:1.
 19. A process for preparing apolydiene, the process comprising the step of: forming a polymerizationmixture by introducing a nickel-based catalyst system and a modulatingLewis base to conjugated diene monomer, where the polymerization mixtureincludes less than about 20% by weight of organic solvent, and where themodulating Lewis base is introduced directly and individually to theconjugated diene monomer, where the nickel-based catalyst system isintroduced to the conjugated diene monomer prior to the modulating Lewisbase and the modulating Lewis base is added to the conjugated dienemonomer before 5% of the monomer is polymerized, or where the modulatingLewis base is introduced to the conjugated diene monomer prior to thenickel-based catalyst system, and where the polydiene has acis-1,4-linkage content of at least 97%, a 1,2-linkage content of lessthan 1.0%, a molecular weight distribution of less than 3.0, a Mooneyviscosity (ML₁₊₄@100° C.) of less than 60, and a gel content of lessthan 20% by weight, where the nickel-based catalyst system is thecombination or reaction product of (a) a nickel-containing compound, (b)an alkylating agent, and (c) a fluorine source, and where the molarratio of the alkylating agent to the nickel-containing compound is fromabout 10:1 to about 50:1, and where the molar ratio of the mole offluorine atoms in the fluorine source to the mole of nickel atoms in thenickel-containing compound is from about 70:1 to about 130:1.
 20. Theprocess of claim 19, where the nickel-based catalyst system isintroduced to the conjugated diene monomer prior to the modulating Lewisbase.
 21. The process of claim 19, where the modulating Lewis base isintroduced to the conjugated diene monomer prior to the nickel-basedcatalyst system.
 22. A process for producing a polydiene, the processcomprising the step of: polymerizing conjugated diene monomer in thepresence of a catalytically effective amount of an active nickel-basedcatalyst and a modulating Lewis base, where the modulating Lewis base isintroduced directly and individually to the conjugated diene monomer,and where said step of polymerizing takes place within a polymerizationmixture that includes less than 20% by weight of organic solvent basedon the total weight of the polymerization mixture, where thenickel-based catalyst system is introduced to the conjugated dienemonomer prior to the modulating Lewis base and the modulating Lewis baseis added to the conjugated diene monomer before 5% of the monomer ispolymerized, or where the modulating Lewis base is introduced to theconjugated diene monomer prior to the nickel-based catalyst system, andwhere the polydiene has a cis-1,4-linkage content of at least 97%, a1,2-linkage content of less than 1.0%, a molecular weight distributionof less than 3.0, a Mooney viscosity (ML₁₊₄@100° C.) of less than 60,and a gel content of less than 20% by weight, where the nickel-basedcatalyst system is the combination or reaction product of (a) anickel-containing compound, (b) an alkylating agent, and (c) a fluorinesource, and where the molar ratio of the alkylating agent to thenickel-containing compound is from about 10:1 to about 50:1, and wherethe molar ratio of the mole of fluorine atoms in the fluorine source tothe mole of nickel atoms in the nickel-containing compound is from about70:1 to about 130:1.
 23. The process of claim 1, where the polydiene hasa cis-1,4-linkage content of at least 98%, a molecular weightdistribution of less than 2.6, a Mooney viscosity (ML₁₊₄@100° C.) ofless than 50, and a gel content of less than 3% by weight.
 24. Theprocess of claim 19, where the polydiene has a cis-1,4-linkage contentof at least 98%, a molecular weight distribution of less than 2.6, aMooney viscosity (ML₁₊₄@100° C.) of less than 50, and a gel content ofless than 3% by weight.
 25. The process of claim 22, where the polydienehas a cis-1,4-linkage content of at least 98%, a molecular weightdistribution of less than 2.6, a Mooney viscosity (ML₁₊₄@100° C.) ofless than 50, and a gel content of less than 3% by weight.
 26. Theprocess of claim 1, where said step of charging a nickel-based catalystsystem to the conjugated diene monomer takes place prior to said step ofcharging a modulating Lewis base to the conjugated diene monomer, andsaid step of charging a modulating Lewis base takes place before 5% ofthe conjugated diene monomer is polymerized, and where the polydiene hasa cis-1,4-linkage content of at least 97%, a 1,2-linkage content of lessthan 1.0%, a molecular weight distribution of less than 3.0, a Mooneyviscosity (ML₁₊₄@100° C.) of less than 60, and a gel content of lessthan 20% by weight.
 27. The process of claim 1, where said step ofcharging a modulating Lewis base to the conjugated diene monomer takesplace prior to said step of charging a nickel-based catalyst system tothe conjugated diene monomer, and where the polydiene has acis-1,4-linkage content of at least 97%, a 1,2-linkage content of lessthan 1.0%, a molecular weight distribution of less than 3.0, a Mooneyviscosity (ML₁₊₄@100° C.) of less than 60, and a gel content of lessthan 20% by weight.